Goodwill and Intangible Assets, net - Schedule of Changes in Goodwill (Details) $ in Millions	3 Months Ended
	Sep. 30, 2025 USD ($)
Goodwill [Roll Forward]
Balance at June 30, 2025	$ 3,273.5
Additions and other adjustments	4.8
Currency translation adjustments	(3.1)
Balance at September 30, 2025	3,275.2
Employer Services
Goodwill [Roll Forward]
Balance at June 30, 2025	3,268.7
Additions and other adjustments	4.8
Currency translation adjustments	(3.1)
Balance at September 30, 2025	3,270.4
PEO Services
Goodwill [Roll Forward]
Balance at June 30, 2025	4.8
Additions and other adjustments	0.0
Currency translation adjustments	0.0
Balance at September 30, 2025	$ 4.8